This application is related to a co-pending application Ser. No. 585,861, filed on Mar. 2, 1984.
This invention relates generally to air/fuel ratio control for an internal combustion engine, and more particularly to a feedback control of the same.
It is generally known that noxious components within exhaust gases of an internal combustion engine can be reduced when the air/fuel ratio of an air-fuel mixture supplied to the engine is set to a stoichiometric value and a three-way catalytic converter is used. Therefore, if an engine is operated in various modes at such a stoichiometric air/fuel ratio using a three-way catalytic converter, then exhaust gases include less noxious components to an ideal extent. However, when an engine is operated at such a stoichiomentric air/fuel ratio throughout all operating modes thereof, increase in fuel comsumption results, and therefore such a simple approach is not advantagous in view of fuel cost. In actual practice, internal combustion engines of automobiles are operated with a rich mixture, such as A:F nearly equals 13, in accelerating mode (high load operating mode), and with a lean mixture in cruising mode (partial or mediam load operating mode).
In the case of an engine with a supercharger, a rich mixture is sometimes fed to the engine for cooling the same for preventing possible temperature raise. In such a case, it is necessary to control the A/F ratio with high accuracy so as to prevent misfiring which is caused from execessively rich mixture.